driver testing [resolved]

joralieu · 2026

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Offline joralieu

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on: April 19, 2024, 12:46:58 PM
Driver testing I have 513 on 1A and 152 on OA also the LEDs on the B side are both out. It's the same for the A and D socket. Where do I look first.
« Last Edit: May 11, 2024, 07:05:12 AM by Paul Birkeland »



Offline Paul Birkeland

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Reply #1 on: April 19, 2024, 02:38:47 PM
I would post some photos of your build so far.  The 152V at OA could be related to the zener diode installation on the 5 lug terminal strips behind the 9 pin sockets, but I would bet on a missing jumper or a jumper going somewhere it shouldn't be on the PC board itself.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline joralieu

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Reply #2 on: April 20, 2024, 04:21:25 AM
Here are some photos



Offline Paul Birkeland

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Reply #3 on: April 20, 2024, 05:41:14 AM
It would likely be best to remove one of the boards, flip it over, and show a picture of the bottom as well.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline joralieu

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Reply #4 on: April 20, 2024, 03:06:25 PM
Another thought, I had my LM431A's in backwards. I desolderd them and turned them. Could that be the problem?





Offline joralieu

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Reply #5 on: April 20, 2024, 07:05:24 PM
Also had the JC29  backwards, had desolder and resolder them. Wonder if I may have damaged something in the process



Offline Paul Birkeland

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Reply #6 on: April 21, 2024, 05:42:08 AM
Did you swap the PN2907 with the 431, or did you install them all backwards?  If you put them in backwards and powered up the amp, then you will need to replace all of those parts.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline joralieu

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Reply #7 on: April 21, 2024, 06:58:11 AM
They were all in the right place but I had the flat sides facing the wrong way. I corrected that before It was powered up.



Offline Paul Birkeland

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Reply #8 on: April 21, 2024, 10:18:19 AM
What are you Kreg voltages? 

Even if not powered up, reworking these boards can be tough.  Still, you have the exact same problem on both boards, so the same error is likely present on both sides.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline joralieu

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Reply #9 on: April 21, 2024, 02:24:37 PM
Socket A        Socket D

Kreg A 4.1.     Kreg A .06
Kreg B 1.8.      Kreg B 1.8



Offline Paul Birkeland

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Reply #10 on: April 21, 2024, 03:12:39 PM
Both B side Kreg voltage indicate saturation, which would make me very, very interested in seeing the bottom of each C4S PC board.  I would wonder if there are solder bridges present between pins on some of the transistors that got swapped around.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline joralieu

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Reply #11 on: April 22, 2024, 04:47:44 PM
Here is the bottom side.



Offline Paul Birkeland

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Reply #12 on: April 23, 2024, 04:31:34 AM
Could you double check that you have the 2.49K and 249K resistors in the correct places.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline joralieu

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Reply #13 on: April 23, 2024, 11:17:04 AM
That's It, those are in the wrong places. Would powering that way damage anything?



Offline Paul Birkeland

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Reply #14 on: April 23, 2024, 02:45:33 PM
It's quite possible that the 431 regulators may need to be replaced on that side of the board, but you can power it up and see.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man